Bulk Materials — Anisotropy, Layer Structure, Dimensionality, Pinning and Critical Current

1992 ◽  
pp. 283-307
Author(s):  
J. Gilchrist ◽  
B. Giordanengo ◽  
J. L. Genicon ◽  
A. Sulpice ◽  
R. Tournier ◽  
...  
Keyword(s):  
Critical Current ◽  
Layer Structure ◽  
Bulk Materials

Structure and Functional Properties of Bulk MgB2 Superconductors Synthesized and Sintered under Pressure

2014 ◽  
Vol 792 ◽  
pp. 21-26 ◽  
Author(s):  
Tatiana Prikhna ◽  
Michael Eisterer ◽  
Wolfgang Gawalek ◽  
Athanasios G. Mamalis ◽  
Artem Kozyrev ◽  
...  
Keyword(s):  
Critical Current ◽  
Material Structure ◽  
Bulk Materials ◽  
Critical Fields ◽  
Current Densities ◽  
Upper Critical Fields ◽  
Irreversibility Fields ◽  
Grain Boundary Pinning ◽  
Effect Of Oxygen ◽  
Oxygen Impurities

The high pressure (50 MPa - 2 GPa) – high temperature synthesized MgB2 bulk materials are characterized by nearly theoretical density (1-2% porosity), 80-98% connectivity, extremely high critical current densities (e.g. at 20 K, in 0–1 T jc=1.3–1.0 MA·cm-2 (with 10% SiC) and jc= 0.92 – 0.73 MA·cm-2 (without doping)), large irreversibility fields (Birr(18.4 K) =15 T and Birr (0 K) = 32.5 T) and high upper critical fields (Bc2 (22 K) =15 T and Bc2(0 K) ~ 42.1 T). The transformation of grain boundary pinning to point pinning in MgB2-based materials with increasing manufacturing temperature (from 800 to 1050 oC) under pressures from 0.1 to 2 GPa correlates well with an increase in critical current density in low external magnetic fields caused by the redistribution of boron and the oxygen impurities in the material structure. As the manufacturing temperature increases, the discontinuous oxygen enriched layers transform into distinct Mg-B-O inclusions and the size and amount of inclusions of higher magnesium borides MgBX (X>4) are reduced. The effect of oxygen and boron redistribution can be enhanced by Ti or SiC additions.

scholarly journals Experimental Study on Ferromagnetic Shunt Effects on the Critical Current of BSCCO Tape in Stacked Conductors

2017 ◽  
Vol 2017 ◽  
pp. 1-7 ◽  
Author(s):  
J. Sun ◽  
H. Ohara ◽  
S. Yamaguchi
Keyword(s):  
Magnetic Field ◽  
Critical Current ◽  
Layer Structure ◽  
Strong Dependence ◽  
Critical Currents ◽  
Ferromagnetic Materials ◽  
Field Analysis ◽  
Test Facility ◽  
Feeding Mode ◽  
Magnetic Field Analysis

In the 200 m high temperature superconducting (HTS) cable test facility at Chubu University constructed in 2010, a three-layer structure of the tapes in the cable is employed for obtaining the high current capacity up to 2 kA. Previous study shows that the critical current is affected by the layout of the tapes such as gaps and the current feeding mode. In the stacked tape conductors, the critical current of BSCCO tapes shows strong dependence on the current feeding directions between the tapes. The critical current is improved when the opposite-direction current is applied to them and degraded for the same-direction current feeding mode because of strong magnetic field interaction between them from the transport current in each tape. This paper presents the measurements of the critical currents of a BSCCO tape in the stacked conductors with the ferromagnetic materials. By using the ferromagnetic materials surrounding the tapes, self-field of HTS tapes is affected and their critical currents are improved by more than 10%. Ferromagnetic shunt effects on the critical current of HTS tape are reported through the magnetic field analysis.

Interfaces in high-temperature superconductors

1992 ◽  
Vol 50 (1) ◽  
pp. 234-235
Author(s):  
K.L. Merkle ◽  
Y. Gao
Keyword(s):  
High Temperature ◽  
Critical Current ◽  
Weak Link ◽  
High Temperature Superconductors ◽  
Atomic Scale ◽  
Bulk Materials ◽  
Practical Applications ◽  
Metallic Contacts ◽  
Zero Resistance ◽  
Interfacial Characteristics

After the discovery of high-temperature superconductors (HTS) five years ago, it soon became apparent that their interfacial characteristics would play an extremely important role in any foreseeable applications of these materials. In recent commercial devices, the weak-link characteristics of grain boundaries (GBs) have in fact been exploited to manufacture Josephson junction SQUIDS. On the other hand, the low critical current density of HTS is a considerable limitation for practical applications of the zero-resistance property, particularly in bulk materials. The weak-link behavior of GBs is largely responsible for this, but other types of interfaces such as those formed by metallic contacts or the interfaces between the substrate and a HTS thin film are also critical to the application of these materials. We shall review here some of the important interface issues that have been addressed by TEM techniques, but shall focus largely on the connection between the critical current (Jc) that can be transported across a grain boundary and its atomic-scale structure and composition.

Synthesis of Unidirectionally Solidified Y‐Ba‐Cu‐0 Bulk Superconductors with High Critical Current Densities

1989 ◽  
Vol 169 ◽  
Author(s):  
E. Yanagisawa ◽  
S. Kondoh ◽  
J. Shimoyama ◽  
J. Kase ◽  
T. Matsubara ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Critical Current ◽  
Applied Magnetic Field ◽  
Bulk Materials ◽  
Large Plate ◽  
Bulk Superconductors ◽  
Plate Shape ◽  
Current Densities ◽  
Melt Solidification

Abstract(Y,Ho)‐Ba‐Cu‐0 superconductors with the high critical current densities (Jc) in an applied magnetic field have been synthesized by a unidirectional melt solidification method. Melt solidified bulk materials are composed of large plate‐shape (Y,Ho)Ba2Cu3Oy crystals which contain small (∼5 um) particles of (Y.Ho)2BaCuO5. The Jc value of the melt solidified (Y,Ho)‐Ba‐Cu‐0 sample is ∼10000 A/cm2 at 77K, H = IT and this value is much higher than the value of 4200 A/cm2 of the melt solidified Y‐Ba‐Cu‐O sample.

Backscattered Electron Imaging of GaAs/AlGaAs Super Lattice Structures with an Ultra-High- Resolution SEM

1988 ◽  
Vol 46 ◽  
pp. 204-205
Author(s):  
Kazumichi Ogura ◽  
Michael M. Kersker
Keyword(s):  
High Resolution ◽  
Layer Structure ◽  
High Sensitivity ◽  
Beam Current ◽  
Electron Beam Current ◽  
Lattice Structures ◽  
Super Lattice ◽  
Different Types ◽  
Backscattered Electron ◽  
Electron Imaging

Backscattered electron (BE) images of GaAs/AlGaAs super lattice structures were observed with an ultra high resolution (UHR) SEM JSM-890 with an ultra high sensitivity BE detector. Three different types of super lattice structures of GaAs/AlGaAs were examined. Each GaAs/AlGaAs wafer was cleaved by a razor after it was heated for approximately 1 minute and its crosssectional plane was observed.First, a multi-layer structure of GaAs (100nm)/AlGaAs (lOOnm) where A1 content was successively changed from 0.4 to 0.03 was observed. Figures 1 (a) and (b) are BE images taken at an accelerating voltage of 15kV with an electron beam current of 20pA. Figure 1 (c) is a sketch of this multi-layer structure corresponding to the BE images. The various layers are clearly observed. The differences in A1 content between A1 0.35 Ga 0.65 As, A1 0.4 Ga 0.6 As, and A1 0.31 Ga 0.69 As were clearly observed in the contrast of the BE image.

Generation of 4H and 6H Structures During the Hexagonal-Rhombohedral Transformation in Dy2Co17

1975 ◽  
Vol 33 ◽  
pp. 38-39
Author(s):  
C. W. Allen ◽  
D. L. Kuruzar
Keyword(s):  
Elevated Temperatures ◽  
Layer Structure ◽  
Transition Element ◽  
Temperature Structure ◽  
Allotropic Transformation ◽  
Layer Plane ◽  
Planar Defects ◽  
Topologically Close Packed ◽  
Transformation Mechanisms ◽  
Shear Transformation

The rare earth/transition element intermetallics R2T17 are essentially topologically close packed phases for which layer structure models have already been presented. Many of these compounds are known to undergo allotropic transformation of the type at elevated temperatures. It is not unexpected that shear transformation mechanisms are involved in view of the layering character of the structures. The transformations are evidently quite sluggish, illustrated in furnace cooled Dy2Co17 by the fact that only rarely has the low temperature rhombohedral form been seen. The more usual structures observed so far in furnace cooled alloys include 4H and 6H in Dy2Co17 (Figs. 1 and 2) . In any event it is quite clear that the general microstructure is very complicated as a consequence of the allotropy, illustrated in Fig. 3. Numerous planar defects in the layer plane orientation are evident as are non-layer plane defects inherited from a high temperature structure.

Microstructural characterization of YBa2Cu3O7-x thin films formed by metalorganic CVD

1991 ◽  
Vol 49 ◽  
pp. 1080-1081
Author(s):  
P. Lu ◽  
W. Huang ◽  
C.S. Chern ◽  
Y.Q. Li ◽  
J. Zhao ◽  
...  
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Film Growth ◽  
Chemical Vapor ◽  
Microstructural Characterization ◽  
Ion Milling ◽  
Conventional Grinding

The YBa2Cu3O7-x thin films formed by metalorganic chemical vapor deposition(MOCVD) have been reported to have excellent superconducting properties including a sharp zero resistance transition temperature (Tc) of 89 K and a high critical current density of 2.3x106 A/cm2 or higher. The origin of the high critical current in the thin film compared to bulk materials is attributed to its structural properties such as orientation, grain boundaries and defects on the scale of the coherent length. In this report, we present microstructural aspects of the thin films deposited on the (100) LaAlO3 substrate, which process the highest critical current density.Details of the thin film growth process have been reported elsewhere. The thin films were examined in both planar and cross-section view by electron microscopy. TEM sample preparation was carried out using conventional grinding, dimpling and ion milling techniques. Special care was taken to avoid exposure of the thin films to water during the preparation processes.

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